WASHINGTON--A top-ranking State Department official yesterday bluntly challenged President Reagan's assurances that there's been no recent evidence of Iranian involvement in terrorism, while Reagan defended anew his decision to approve arms shipments to Tehran.

"I don't like to have to differ with my president, but I believe there is some evidence of Iranian involvement with terrorists," Deputy Secretary of State John C. Whitehead said during an extraordinary appearance before the House Foreign Affairs Committee.

While Whitehead testified, Reagan said from the White House, "I didn't make any mistakes" and declared that "I'm not firing anybody." The president then sat down with members of his Cabinet and top advisers to weigh new moves, amid a crescendo of calls by members of Congress for a White House shakeup.

In statements that left some House committee members stunned, Whitehead, the number two State Department official under Secretary of State George Shultz, also suggested pointedly that Congress rein in the National Security Council, and said publicly that his department was disenchanted with the unit.

In his nationally broadcast speech November 13th, Reagan defended his policy of selling arms to Iran, saying that "since U.S. government contacts began with Iran, there's been no evidence of Iranian government complicity in acts of terrorism against the United States."

Whitehead contradicted that yesterday.

Responding to the committee's questions, he said: "There continues to be terrorist acts in Iran of the type that we find to be reprehensible."

State Department spokesmen had been saying for weeks that while Iran remained on a list of nations officially identified as "terrorist-sponsoring states," they would not provide evidence that nation has sponsored any recent terrorist acts.

On Friday, however, Whitehead, and other State Department officials speaking privately, linked Iranian-sponsored groups to the kidnapping of three Americans seized in Beirut since September 9th.

A department official, speaking on condition he not be identified, said the United States was initially unsure who was responsible for some of the recent kidnappings because a group unknown to terrorism experts--the Revolutionary Justice Organization--had claimed responsibility.

Subsequently, the department has received "pretty good" information that pro-Iranian factions are behind the kidnappings, the official said.

During a picture-taking session in the Oval Office, Reagan made no secret of his unhappiness over news reports about back-biting among his staff, calls for resignations, and suggestions that he admit the Iranian initiative was a mistake.

"I think you'd be happier if I said I'd stop answering questions on that because you wouldn't like my answers," the president told reporters.

Even so, he said, "I'm not firing anybody." Pressed on whether there would be any staff changes, Reagan said, "I'm not commenting either way."

During his testimony to the House panel, Whitehead lashed out against the National Security Council for masterminding the secret contacts with Iran, which led to the sales of arms.

"We in the State Department find it difficult to cope with the National Security Council's operational activities," he testified.

Whitehead said the department welcomes the council's advisory role.

"But when they become involved in operational matters we have concerns, particularly when we don't know about them," he testified.